Almost nothing – not even bariatric surgery – changes olfactory sensitivity

Altered olfactory functions during hunger, fasting episodes, and following food ingestion in healthy subjects have been reported as early as 1949 but subsequent data have remained controversial.

Methods: We investigated olfactory function (threshold, identification, discrimination) (Sniffin Sticks®) in six independent experiments: At baseline and 24h and 48h after a zero calorie fasting (n=16 females) (Study 1); fasted and after a 900kcal mixed meal (n=20 males) (Study 2); twice after a 600kcal mixed meal with high (40g) saturated or unsaturated fatty acids (n=24, 12 females) (Study 3); prior to and after rotation-induced nausea (n=44 males) (Study 4); at baseline and after a 5-day 6° head-down tilt bedrest (HDT-BR) and a high (7.7 mmol/kg BW/d) and low (0.7 mmol/kg BW/d) sodium diet (n=8 males) (Study 5). We also compared odor sensitivity before and 12 months after bariatric (sleeve) surgery in 8 patients (4 females) with morbid obesity (Study 6).

Results: Fasting (Study 1) did not alter olfactory functions, but a high-calorie diet (Study 2) significantly improved odor discrimination only; saturated fatty acids (Study 3) improved odor identification significantly, while the induction of nausea (Study 4) did not affect olfaction. HDT-BR (Study 5) significantly reduced the olfactory thresholds as well as the total score, mainly due to the bedrest component. Bariatric surgery (Study 6) did not change odor sensitivity, but some morbidly obese exhibited abnormally low olfactory functions prior to and after surgery.

Conclusions: Manipulation of the hunger/satiety state has only marginal effects on olfactory functions in normal healthy volunteers.

(Supported by grants from Zentrum für Ernährungsmedizin Tübingen & Hohenheim).